Experiment On Solid Retrograde Eclogite And Amphibolites From Dabie UHPM Belt

This study presents the open and dehydration melting experiments on one solid retrograde eclogite and three amphibolites from Dabie UHPM belt, Dongchonghe in Yingshan, Hubei province. The experiments are at 0.1Gpa and 750℃, 800℃, 850℃ and 900℃. The duration time for heating is 4 hours. Hydraous minerals in retrograde eclogite are biotite and hornblende, and in three amphibolites are chlorite, biotite and hornblende which have partly retrograde to biotite.The partial melting process of retrograde eclogite and three amphibolites are the same. The initial melting commences from dehydration melting of hydrous minerals. At close system, the H₂O dissolved by hydrous minerals directly join in melting process. It can decrease melting point, and induce the priority melting of felsic minerals. The composition of initial melts is acid. But for the open system, the H2O dissolved by hydrous minerals will be released and be out of the system. So the priority melting of minerals are hydrous minerals. The composition of initial melts, which melting felsic minerals, is basic.For retrograde eclogite, there are no melts at 750℃ and 800℃, about 15% melts at 850℃ and 45% at 900℃ . Melts are mainly in the three localized melting systems. They are the grain boundaries of symplectite, the grain boundaries and cracks of quartz, and one side of sample on which is higher melting degree. Because of different compositions of minerals in different localized melting systems, chemical compositions of melts range from basic to acid at the same temperature. And at the same localized melting system, compositions of melts run to acid along with the increase of temperature. At different temperature, composition exchange occurs at the grain boundaries of garnet. Na primarily displaces Ca and Mg into crystal lattice of the grain boundaries of garnet. In symplectite, with increasing temperature, the An content of plagioclase trend to be increase, and the composition of hornblende trends to be clinopyroxene.For three amphibolites, which number are 21DB19-4, 21DB23-2 and 21DB23-3, there are no melts at 750℃ and 800℃, and a little melts at 850℃. At 900℃, the degree of partial melting of 21DB23-3 sample is the highest and the melts are about 45%. The melts of 21DB19-4 sample...